Homemade rim thickness gauge

[TOP PREDATOR]

The reasoning behind sorting rimfire ammunition by rim thickness sounded very valid to me. The concept is that headspacing varies when the thickness varies, and since rimfire ammo headspaces on the rim of the cartridge, if you can take out the variances by measuring and lotting "like" thicknesses, you will improve accuraccy. Just as in reloading, differing overall lengths and seating depths produce differing results, hampering steady consistancy.

Enter the rim thickness gauge.

As always looking for a way to economically improve performance, I finally decided to purchase a rim thickness gauge. I did a search on the net to find manufactures when I cam across a froum thread on making your own rim thickness gauge. After reading it, I immediately went to my reload bench to get started, and after just a few minutes, put together my own thickness gauge.

Items needed: calipers, and one spent or new .243 case. In the original thread, the gentleman used a .223 case, which seemed a natural choice, but I found that it scrapped off the valuable lubrications on rimfire ammo. So I went with .243. I also had some 3M non skid stick on material around so I thought I'd use it also.

I took the casing and put it on the trimmer to give it a nice flat and even lip. Ironically I used the same calipers used for the rim thickness gauge to so several measurements while turning the casing to ensure it is as flat and even as I can get it. I then took a neck brush to clean the inside of the neck of any residue. I shined the brass up a bit with never dull (for looks) and wrapped the non skid around the casing for grip and to designate it as a casing I want to keep for a special purpose.

I then simply put the casing in the calipers, closed the jaws and zeroed out the calipers.

To measure rim thickness on rimfire ammo, just slip the rimfire round into the opening of the case. The mouth of the .243 case bumps up against the rim and is not too wide as to allow the rimfire case from falling in the .243 case.

Now just put the calipers back on the .243 case with the rimfire case in it and take a measurement. The reading is the rim thickness.

My first 3 measurements....

Now to weigh a few more and see if the concept is real, which means another one of my long winded ammo tests. Will be updating with results soon.

 

[The Mechanic]

Re: Homemade rim thickness gauge

Friggin' genius. Good job.

 

[TOP PREDATOR]

Re: Homemade rim thickness gauge

i can't take the credit, just copying what i seen elsewhere. except of course replacing the .223 casing with a .243 to keep the lube on the heand and not to distort the head in any manner.

i imagine this will work with .22 mag, .17hmr, etc.

 

[benwitt11]

Re: Homemade rim thickness gauge

Makes a heck of a lot of sense to me. Thanks for bringing it up again. I'd read about this. A while ago but had forgotten about it.

 

[Greg Langelius *]

Re: Homemade rim thickness gauge

Tag.

 

[caustic]

Re: Homemade rim thickness gauge

I'm interested in the groups achieved with measured only v.s. weighed and measured, like TP said to see if the concept is real. but none the less a good and simple idea.

 

[donws2]

Re: Homemade rim thickness gauge

I'm very interested in the results as well. I've done the same test several times. I'll hold off repeating my results so as not to influence this test. I will however give the outline of how I did my test. I used ammo from only the same lot to run a test to start with. I shot ten five shot groups with the ammo straight from the box at fifty yards. I then shot ten five shot groups with Rim measured only, Weight separated only and Rim and weighed only. All I did for rim separating is pull the 10 or 20% of thin and fat rims out and make two groups out of the rest. You’ll end up shooting allot of weight separated groups because there will be clusters of weighed bullets in the middle. Let’s say the spread is 49.2 to 52.0 for 500 rounds weighed. There will be groups of 49.7 to 49.9, 51.1 to 51.2 and 51.3 and 51.5. If you graph out the results it looks like a sign wave with peaks and valleys. I use small parts bins to hold the weighed ammo until I have enough to fill a box. I then group them together with no more than .2 grains difference per test lot. All ammo outside the center range is used to foul the barrel after cleaning and get a rough zero. I clean the barrel after each test of ten groups and re-foul the barrel with twenty shots. I believe that between Rim, Weight and Rim and Weight separated ammo you will find some very interesting results.

Donald

 

[The Mechanic]

Re: Homemade rim thickness gauge

Anybody got a spare .243 case? I'll pay shipping and a little extra. Looked through all my brass and don't have a single piece.

 

[jcwarrior87]

Re: Homemade rim thickness gauge

i have a crap load of it, pm me your address, I'll try to get you one out in a week

 

[caustic]

Re: Homemade rim thickness gauge

Hey T.P. any data yet?

 

[TOP PREDATOR]

Re: Homemade rim thickness gauge

not yet i had some stuff that i was obligated to do this past weekend and a silhouette match. i hope to do something this weekend, if the wind is light to get a better baseline.